This application claims priority of German Patent Application Number 198 59 133.0-41, filed Dec. 21, 1998, the entire disclosure of which is considered to be part of the present disclosure and is specifically incorporated by reference herein.
The present invention relates to an ejection device for the high-pressure ejection of a liquid or a liquid containing solid particles, comprising a head unit and a pressure chamber which opens into a distal ejection opening and is delimited by a working piston which, upon application of an elastic impact on its end facing away from the pressure chamber, is capable of transmitting a compression wave by which the pressure chamber-facing end of the working piston is displaceable into the pressure chamber so that the volume thereof is reduced. The reduction in volume of the pressure chamber is significantly smaller than the volume of the pressure chamber resulting in high-pressure ejection of a small quantity of the liquid through the ejection opening. Further, the ejection device comprises a drive unit having a drive member which is accelerated along an acceleration portion within the drive unit to generate the elastic impact to be transmitted to the working piston.
Ejection devices of the above described type are known, for example, from EP 771 219, which describes said devices as being specially designed for the ejection of precisely dosed, minute amounts of liquid, which may be in the range of cubic millimeters, so that these devices are particularly well-suited as medical instruments for the injection of minute doses of liquid drugs which are to be administered with high precision.
The ejection of such small amounts of liquid is achieved by the drive member transmitting only an elastic impact to the working piston so that the latter is not moved any further into the pressure chamber by the drive member. That is, after having transmitted the impact, the drive member no longer exerts any external driving force upon the working piston so that the amount of liquid contained in the pressure chamber and defined by the working piston is not ejected in the way it would in a common syringe, but exclusively by means of the compression wave excited by the impact transmitted through the working piston. The compression wave propagates into the pressure chamber and causes the liquid to be ejected from the ejection opening at high pressure. The ejection pressure, and thus the volume or amount of liquid ejected from the opening, may be precisely controlled by suitably adjusting the velocity of the drive member since this velocity determines the magnitude of the impact which is transmitted.
According to the ejection devices described in EP 0 771 219, the volume of the pressure chamber considerably exceeds the stroke volume of the working piston so that a small, precisely dosed amount of liquid may be ejected regardless of the actual size of the pressure chamber.
To prevent the drive member from exerting any external force on the working piston after the impact has been transmitted, it is possible, for example, to stop the application of a driving force acting on the drive member towards the working piston as soon as the transmission of the impact starts, or to provide a stopper which prevents the drive member from transmitting any force to the working piston after the impact has been transmitted.
The working piston is preferably made of a solid material which transmits elastic shock waves with as little loss as possible, such as a metallic material. The drive member may be any component which can be accelerated across an acceleration portion, such as a drive piston which may be accelerated within a drive pipe and is preferably coaxially aligned with the working piston. However, the drive member may also be designed other than as a piston, for example as a plate or a rocker arm which acts upon the working piston so that a driving impact is exerted thereupon.
The drive member may be driven pneumatically, hydraulically, mechanically, or electromagnetically. The means driving the drive member may be designed such that they enable only a single working stroke of the drive member. However, the drive member may preferably be driven such that it successively transmits periodically repeated impact pulses so that the total amount of liquid being ejected may be controlled by suitably adjusting the number of repetitions.
In the endoscopic version known from EP 0 771 219, the working piston is formed as a probe extending within the endoscopic catheter and having a proximal probe head arranged in an acceleration pipe. The acceleration pipe accommodates a working piston which acts upon the probe head so that a compression wave is excited within the probe that causes the end of the probe located in the catheter to be displaced into the pressure chamber formed by the lumen of the catheter, so that liquid is ejected.
However, the ejection devices known from EP 0 771 219 are difficult to clean and sterilize because of the integral structure of their head units containing the liquid to be ejected.
The present invention provides an ejection device of the initially mentioned type whose head unit may be easily cleaned and sterilized, and which at the same time enables an adequate protection of the liquid to be ejected from contamination, and in particular from any contamination caused by the drive unit of the device.
According to the present invention, the pressure chamber of the ejection device is at least partially formed by a pressure cavity provided in the head unit of the device. Furthermore, the head unit and the drive unit of the device are formed as separate, independent units which are mounted to each other by means of a separable mounting coupling. Further, an intermediary member is provided between the working piston and the acceleration portion, which is formed as a separate component and transmits the elastic impact from the drive member to the working piston. Said intermediary member is arranged in the drive unit of the device and provides a tight seal between the acceleration portion of the drive unit and the working piston.
Since the head unit and the drive unit of the ejection device according to the present invention are designed as separate units which are separably connected to each other, the head unit containing the liquid to be ejected may be easily and separately cleaned and sterilized. The drive unit requires either no sterilization at all, or only local sterilization at its end facing the head unit. Since said two units of the ejection device are separately sealed, and since especially the acceleration portion of the drive unit is sealed against the head unit, any contamination of the liquid accommodated in the head unit by dirt particles or pathogens present in the drive unit is safely prevented. Further, it is possible to easily and, thus, quickly replace the head unit by another one containing a different liquid drug, for example.
In the ejection device according to the present invention, the impact is transmitted via the intermediary member which is acted upon by the drive member. When the drive member abuts against the intermediary member, a shock wave is excited within the intermediary member which propagates therethrough and is transmitted by the intermediary member to the working piston which in turn transmits the shock wave into the liquid contained in the pressure chamber. The intermediary member is particularly advantageous since it transmits the impact to the working member while remaining itself in a stationary position, provided that it has been designed with a suitable mass and abuts against the working piston preferably without play. In this way, the sealing of the acceleration portion achieved by means of the intermediary member is ensured also during impact transmission.
This sealing principle for impact drives is also described in DE 196 18 971 A1, although in connection with a kidney stone crusher.
The intermediary member is preferably made of a solid material which transmits elastic shock waves possibly without loss, such as a metallic material. Further, the intermediary member is preferably formed as a piston-shaped body, and its axial motion is limited by stoppers in both directions, with a small axial play being allowed between the intermediary member and the stopper which is proximate to the working piston so that any pulse transmission from the intermediary member to the stopper proximate to the working piston is prevented, which ensures a loss-free transmission of impact pulses to the working piston.
According to a preferred embodiment, the head unit comprises a sleeve-type insert which accommodates the working piston and is mounted to the drive unit by means of the separable mounting coupling. A cap is separably mounted to the insert and comprises a pressure cavity outlet that forms the fluid connection with the ejection opening. The pressure cavity may be formed exclusively in the insert, for example by designing the hollow provided in the insert to accommodate the working piston with a greater length. However, the pressure cavity may also be formed by a cavity as described above which combines with an adjacent recess formed in the cap.
This two-part structure of the head unit enables it to be disassembled for cleaning and sterilization so that it is more readily accessible for cleaning tools. The connection between the insert and the cap may be formed, for example, by a plug-in connection, a bayonet fastener or a screw-type connection.
Although the propagation of the compression wave and, thus, any leakage of liquid from the pressure chamber may be prevented by minimizing the gap between the cap and the insert, it is preferable to provide an elastic seal which seals the gap between cap and insert so that the liquid is more safely protected from contamination by pathogens, for example. Further, it is also preferable to provide an elastic seal sealing the gap between the insert and the drive unit of the device so that pathogens are effectively prevented from invading between these two parts as well.
To enable a periodic operation of the ejection device according to the present invention, a liquid filling neck is provided which is advantageously formed at the insert and communicates with the pressure cavity via the gap between the working piston and the insert. The gap between the working piston and the insert is large enough to provide a sufficient fluid connection between the pressure chamber and the liquid filing neck, and narrow enough to ensure that the propagation of compression waves excited in the pressure chamber through the gap and rearwardly towards the liquid filling neck is minimized. Further, it is thus not necessary to provide a separate supply passage which would require additional sterilization or had to be provided with a check valve. The liquid filling neck may, for example, be designed as a neck which is inserted or threaded into the side surface of the insert. For this purpose, the insert preferably comprises a radial flange which is formed in the longitudinal center thereof and serves both as a base for the liquid filling neck and as a handle which facilitates the mounting of the insert including the cap to the drive unit. Alternatively, the liquid filling neck may be provided at the cap which in this case comprises a passage formed therein that is controlled by a check valve and connects the pressure chamber to the filling neck.
To improve the efficiency of the ejection device, the working piston is sealed against the insert by means of an elastic sealing element which is arranged around the circumference of the piston at a position behind the liquid filling neck, as seen from the pressure chamber. Said sealing element prevents the leakage of liquid into the drive unit so that the liquid may exit the pressure chamber only through the ejection opening. Furthermore, the sealing element prevents the compression wave from propagating through the gap between the working piston and the insert so that, secondarily, a rearward ejection of liquid from the pressure chamber is prevented.
The elastic sealing element may be arranged, for example, in an inner annular groove formed in the insert so that it sealingly abuts against the circumference of the working piston. However, according to a preferable embodiment, the end of the working piston which is distal to the pressure chamber is provided with a radial flange so that the elastic sealing element may be arranged between said flange and a shoulder formed in the insert, at the side of the flange facing the pressure chamber. This design is advantageous because during ejection the elastic sealing element will thus be pressed on by an increased pressure, because the impact transmitted to the piston pushes the piston and its flange towards the shoulder formed in the insert. Thus, the sealing of the pressure chamber is further improved. Further, the sealing element advantageously ensures that the working piston always returns to its original axial position, i.e. the position it had before the impact, which is preferably a position where it abuts against the intermediary member so that the intermediary member is pressed against the stopper distal to the working piston, which ensures that an axial play is maintained between the intermediary member and the stopper proximal to the working piston. Said play is necessary for a trouble-free operation of the device. To enable the discharge of fluid also at times when the device is not operating, the sealing element is advantageously arranged to be elastically biased between the flange and the shoulder formed in the insert. The returning of the working piston together with the intermediary member to their respective original positions may also be ensured by the sealing element arranged in the annular groove formed in the insert as mentioned above, if said sealing element is elastically biased in said groove so that any axial displacement of the working piston relative to the sealing element is prevented.
Preferably, a compensation cavity is provided around the gap between the working piston and the intermediary member and filled with gas such as air, for example. In the case of the working piston being separated from the intermediary member during impact transmission, the space formed between them will create a negative pressure which may interfere with the motion of the working piston. However, since the compensation cavity is larger than the space created between the intermediary member and the piston, this pressure drop is so small that it does not affect the motion of the working piston.
According to an embodiment, the ejection device according to the present invention is formed as an endoscopic ejection device. For this purpose, the head unit of the device is connected to an endoscopic catheter comprising a lumen, which enables the passage of liquid therethrough, and the ejection opening, with the pressure chamber being formed by the lumen of the catheter and by the pressure cavity formed between the lumen and the working piston.
With the embodiment, the formation of at least part of the pressure chamber within the head unit has the advantage that any residues produced by abrasive wear during the motion of the working piston will mainly be found in the head unit rather than within the lumen of the catheter. Thus, there is a decreased risk of particles resulting from abrasion being ejected, and the removal of such particles is easier because the head unit may be designed in such a way as to be more easily accessible by cleaning devices than the elongated, narrow catheter specially designed for insertion. In general, any movable components such as another check valve preventing air from being sucked back into the pressure chamber, for example, may be arranged within the head portion so that the endoscopic catheter only serves as a passage for the liquid and may thus be formed with particularly small dimensions. The head unit may also be connected to different catheters of any desired inner diameter without difficulty, and with the endoscopic device remaining fully functional.
The catheter may be fastened to the head unit, and preferably to the end thereof which is opposite the working piston, by means of a screw-type or plug-in connection, for example. Correspondingly, in the case of a multiple-part version of the head unit comprising the cap, the catheter will advantageously be mounted to the cap. The endoscopic catheter may be formed as a rigid or as a flexible catheter. Furthermore, it may be designed for insertion into the operating passage of an endoscope. For endoscopic applications, the ejection device and the endoscope may preferably be combined to form one single unit.
In view of the prefered use of the device according to the invention, the walls surrounding the pressure chamber and, thus, its surrounding parts such as the insert, cap, working piston and seals should be made of a material which is particularly easy to sterilize any may be kept sterile without difficulty, i.e. they should be made of a very smooth material such as polished steel or titanium or their alloys, for example, which does of course not apply to the seals. Moreover, the materials should be inert with respect to the liquid to be ejected.
To enable the cleaning and sterilization of the device, the mounting coupling may be separated or disconnected so that the head unit may be removed from the drive unit. Next, the working piston may be removed from the insert together with its surrounding sealing element, after which the sealing element may be stripped from the working piston. Further, it is possible to disconnect the cap and the catheter fastened thereto, or the insert and the cap.
To prevent the drive member from accidentally leaving its starting position, a fixing device is provided to fix the drive member at its starting position. The fixing device may be a clamping device, for example, which fixes the drive member by means of clamping forces which may be overcome by the driving forces. Advantageously, a magnetic fixing device is provided for fixing the drive member and formed, for example, by an electromagnet, but preferably by a permanent magnet. The drive member may have magnetic part attached thereto such as a magnetizable metallic member which acts in combination with the magnetic fixing device. Preferably, the entire drive member is made of a magnetizable material such as steel, for example.